This invention relates to a fuel cell separator and its production method, and more particularly, to a fuel cell separator made of conductive material and resin wherein the conducive material is recycled from waste of fuel cell separators, and to a method of producing a fuel cell separator using the material recycled from the waste of fuel cell separators.
A fuel cell which generates electric power by making use of fuel gas and oxidant gas, especially a solid polymer type fuel cell, is considered to be a new clean energy source in various applications including automobiles. A solid polymer fuel cell is configured in such a way that an ion conductive solid electrolyte membrane is sandwiched by an anode and a cathode each having a catalyst and functioning as a gas diffusion electrode, and an outside of each electrode is further provided with a fuel cell separator. The fuel cell separator at the anode provides hydrogen as fuel gas, and the fuel cell separator at the cathode provides oxygen as oxidizer gas.
FIGS. 4(a) and 4(b) show an example of such a fuel cell separator. As shown in FIGS. 4(a) and 4(b), on a fuel cell separator 1, narrow channels 1a are formed on a planar surface thereof. In order to increase an overall surface area for connecting between the gas diffusion electrode and the gas, the channels 1a are meandering with a small pitch on the whole surface of the fuel cell separator. The channels 1a may be formed on both surfaces of the fuel cell separator as shown in FIG. 4(b), or may be formed only on one surface of the fuel cell separator.
There are other types of structures of the fuel cell separator wherein both surfaces or one surface is provided with a large number of projections where spaces between those projections are used as passages of the gas, or both surfaces or one surface is provided with combinations of such projections and channels.
Since the fuel cell separators described above use a large amount of carbon material, a problem arises when such fuel cells are wasted because of their life times or other reasons. Because the waste of the fuel cell separators include a large amount of carbon material as noted above, how to deal with such industrial waste is an important subject in the fuel cell industry.
In this respect, Japanese Patent Laid-Open Publication No. 10-255823 appears to disclose a structure of a fuel cell separator related to this problem. In this patent publication, it is stated that a conventional fuel cell separator made of carbon based bulk material such as artificial graphite or vitrified carbon has drawbacks in that it tends to be damaged by mechanical shocks or vibrations because of its low toughness and it is difficult to recycle. The patent publication proposes a fuel cell separator made of metal which includes aluminum or titanium as base material in a weight ratio of 80% or higher on which a layer of conductive carbon is provided. It is stated, as an effect of the invention, that recycling of the fuel cell separators has become easy because of the structure of the structure thereof.
Although no description is given in this patent publication as to the method of recycling the fuel cell separators, there is a recitation stating that xe2x80x9caluminum is especially preferable for this purpose because of its characteristics of easy recycling, easy machining, and low costxe2x80x9d. Based on this recitation, it is assumed that the invention in this patent publication is directed only to the recycling of the metal components in the fuel cell separator.
In contrast, as noted in the foregoing, the present invention relates to a fuel cell separator which is made of resin and conductive material such as carbon. This fuel cell separator in the present invention is the type of separator designated in the above Japanese Patent Laid-Open Publication No. 10-255823 as the one having the carbon based bulk material and is considered difficult to recycle.
The present invention reflects on the aforementioned facts and conventional technology. It is, therefore, an object of the present invention to provide a fuel cell separator and its production method which can easily recycle the waste of fuel cell separator containing conductive material and resin.
It is another object of the present invention to provide a fuel cell separator and its production method which is capable of decreasing the industrial waste involving the fuel cell separators, thereby improving environmental conditions and saving natural resources.
It is a further object of the present invention to provide a fuel cell separator and its production method which is capable of using the material obtained from the waste of fuel cell separators where the content of the material is always known, thereby enabling to produce fuel cell separators of uniform and high quality.
In order to achieve the objectives above, the fuel cell separator made of conductive material and resin is comprised of conductive material at least a part of which is powdered material made by pulverizing the waste of fuel cell separator which contains conductive material and resin.
The waste of fuel cell separator is converted to carbon or graphite through a baking process which is conducted under baking temperature ranging from 500xc2x0 C. to 3,000xc2x0 C. The conductive material includes carbon powder which has an average diameter ranging from 10 xcexcm to 100 xcexcm. Preferably, the average diameter of the carbon powder is about 30 xcexcm.
Another aspect of the present invention is a method of producing a fuel cell separator which is comprised of a step of crushing the waste of unbaked fuel cell separator containing conductive material and resin, a step of supplementing unused conductive material and/or resin to the crushed waste of unbaked fuel cell separator to form powdered material; and a step of molding the powdered material by a mold under a predetermined molding pressure and temperature to form the fuel cell separator.
Preferably, the production method further includes a step of baking the waste of fuel cell separator, either before or after the crushing step, under baking temperature ranging from 500xc2x0 C. to 3,000xc2x0 C. An environmental gas may be supplied to the powdered material in the baking step. Preferably, the production method further includes a step of adding solvent to the powdered material to granulate the powdered material.